Set Pressure vs. Cold Differential Test Pressure — A Field Guide

The short answer

Cold differential test pressure (CDTP) compensates the bench set point for the temperature and back-pressure the valve will see in service.

Rules of thumb

• For conventional valves, add the superimposed back pressure to the desired set pressure.
• Correct for temperature when service exceeds 120 C, using the manufacturer chart.
• Balanced-bellows valves already negate most back-pressure effects — check the datasheet first.

Common mistakes

Applying CDTP to pilot-operated valves without checking the pilot dome rating, and forgetting that CDTP changes when the process conditions change.